A Sri Lankan soldier walks among debris as the war with the Tamil Tigers came to a close. Photograph: AFP/Getty Images

“It is equal to living in a tragic land/ To live in a tragic time,” said Wallace Stevens in the poem “Dry Loaf”. It is about an attempt to portray a bucolic scene – “That was what I painted behind the loaf,/ The rocks not even touched by the snow” – while the exercise is transformed at every moment by the incursion of history: “It was the soldiers went marching over the rocks/ And still the birds came, came in watery flocks,/ Because it was spring and the birds had to come.” In Samanth Subramanian’s excellent account of the civil war and its aftermath in Sri Lanka, history encompasses the people who lived through that “tragic time”, and the land’s sole function is to serve as that history’s paradigm. There’s no getting away, whether you find yourself in Canada or in a time of peace.

Subramanian is an Indian of Tamil ethnicity. Today’s regrettable recuperation of caste origins in India in the name of genealogy would remind us that he’s a Tamil Brahmin or, in the kitsch-sentimental language of the new Indian elite, which both fetishises and constantly invents pedigree, a “Tam-Brahm”. The Tam-Brahm, progeny of a priestly class, is putatively a secular whizz-kid and achiever, although the upper-caste inflection is never entirely renounced. And, indeed, Tamils have shone in modern India: to take just one instance, India’s remarkable space programme is powered by Tamil scientists.

In Sri Lanka, the Tamils did well, too – through a quirk of colonial policy, says Subramanian, which gave them unfair access to higher education and key institutional positions. So, as is the case with ethnic minorities in other parts of the world, they constituted that unfortunate group that once benefited from the imperial practice of divide and rule. Still, how much of the rise of the Tamils might be attributed to colonial history and how much to their response to modernity isn’t clear. Some of the Tamils’ success in Sri Lanka must surely be the result of the innate and inherited skills that have seen them flourish in the modern world. Might it have to do, partly (as in India), with an upper-caste elite that possessed the ballast of an intellectual history?

Subramanian doesn’t tell us very much about the caste histories of Sri Lanka’s Tamils. What’s clear from his book is how much they were resented by the majority Sinhalese for their privileges. By the 70s, they were being seen as outsiders by a majoritarian Sinhalese nationalism, though Subramanian points out that a foundational Sinhalese Buddhist text, the Mahavamsa, makes it clear that the Tamils had been in Sri Lanka for a couple of millennia. As with German Jews four or five decades before (and with those in Malaysia today who aren’t bumiputras – literally, “sons of the soil”), the educational and political rights of Tamils began, one by one, to be curtailed. These developments engendered the utopian vision of the founder-leader of the Tamil Tigers, Velupillai Prabhakaran – that the north of Sri Lanka be declared an eelam, a separate homeland for Tamils. Prabhakaran was convinced there was no way the Tamils could achieve that utopia without waging war.

Some of this lineage of deprivation and recrimination is confusing to the naive outsider. For instance, the Sinhalese do not seem like a race of underlings: they clearly have the robust and even aristocratic sense of cultural identity that allowed Arjuna Ranatunga, the captain of the Sri Lankan cricket team, to respond to Shane Warne with: “We come from 2,000 years of history. We all know where the Australians come from.” Who’s the “we” here? On the one hand, this might be an expression of Sinhala arrogance. On the other, more plausibly, it could be a non-violent, quasi-Gandhian rebuttal; one wonders, then, why rebuttal, rather than retribution, featured so little in late 20th-century Sri Lankan politics. Was it marginalised by the intransigence (as it appears from Subramanian’s book) of both a new rightwing Buddhism and of Prabhakaran? One also wonders about the intellectual formation of another superb Sinhalese batsman, Kumar Sangakkara, probably the most articulate cricketer the world has seen for a while, and his lofty, classically secularist proclamation: “I am Tamil, Sinhalese, Muslim and Burgher”. Faced with two ethnic groups that possess individuals with great leadership skills, courage and sophistication, one can only speculate why Sri Lanka didn’t have the kind of renaissance that the southern parts of India did with globalisation. Success would have seemed a truer destiny for it than the violent political impasse it inflicted on itself until 2009, when the war ended with the crushing of the Tigers and the death of Prabhakaran.

From 2011, Subramanian spent time in the locations in which the traumatic events – the Tamil word for them is prachanai, problem – gathered momentum; he effaced himself and patiently pursued the participants with questions. He even went to Canada, and interviewed those who were quietly resettled, including a fascinating and implausible subset of Tamils who were officers in the Sri Lankan army. He suffered in the Sri Lankan heat, which appeared to both slow him down and allow him to grasp, as a narrator, the lack of fixity in the dichotomous narrative – about the Sinhalese and the Tamils – he was aiming to tell us. Midway through the book, he fell ill; recovering, he read, with that special blurry focus that comes from being out of sorts, the Mahavamsa, in which he discovered the mythic and minatory figure of Dutugemunu, a precursor to present-day Sinhalese cruelty.

By now, the book’s reportorial tone has given way to a subterranean reality especially characteristic of South Asian epics: that there are no firm moral positions in a war between relatives. If the Sinhalese army was savagely punitive, so was Prabhakaran (who believed in unquestioning fealty) towards his own. This, suggests Subramanian, was essentially how he lost the war, despite having, at one point, almost absolute control over the north: because his pathological distrust of internal opposition, policy of forced conscriptions and fundamental intolerance of democracy alienated his constituency.

Nothing remains of Prabhakaran’s house now except “the absence of a house” where “a cat and a chicken were fighting at the back of a plot”. The crushing of the Tigers and the Tamils is captured by Subramanian with exemplary concision; he himself seems unprepared for the impact the survivors’ stories have had on him: “They would lose their potency ... I had thought at first ... But here they were ... Time had clarified memory, instead of muddying it.” These closing chapters are not so much testimonials as a distillation of what it means to be defeated. The book leaves us with a tantalising sense of the ambiguity of peace and victory: of the new and incongruous conservatism of Sinhalese Buddhism. Subramanian withholds judgment, but the precision of the final descriptions is searing.